org.apache.commons.collections4.map
Class DefaultedMap<K,V>

java.lang.Object
  extended by org.apache.commons.collections4.map.AbstractIterableMap<K,V>
      extended by org.apache.commons.collections4.map.AbstractMapDecorator<K,V>
          extended by org.apache.commons.collections4.map.DefaultedMap<K,V>
All Implemented Interfaces:
Serializable, Map<K,V>, Get<K,V>, IterableGet<K,V>, IterableMap<K,V>, Put<K,V>

public class DefaultedMap<K,V>
extends AbstractMapDecorator<K,V>
implements Serializable

Decorates another Map returning a default value if the map does not contain the requested key.

When the get(Object) method is called with a key that does not exist in the map, this map will return the default value specified in the constructor/factory. Only the get method is altered, so the Map.containsKey(Object) can be used to determine if a key really is in the map or not.

The defaulted value is not added to the map. Compare this behaviour with LazyMap, which does add the value to the map (via a Transformer).

For instance:

 Map map = new DefaultedMap("NULL");
 Object obj = map.get("Surname");
 // obj == "NULL"
 
After the above code is executed the map is still empty.

Note that DefaultedMap is not synchronized and is not thread-safe. If you wish to use this map from multiple threads concurrently, you must use appropriate synchronization. The simplest approach is to wrap this map using Collections.synchronizedMap(Map). This class may throw exceptions when accessed by concurrent threads without synchronization.

Since:
3.2
Version:
$Id: DefaultedMap.java 1479407 2013-05-05 22:07:53Z tn $
See Also:
LazyMap, Serialized Form

Nested Class Summary
 
Nested classes/interfaces inherited from interface java.util.Map
Map.Entry<K,V>
 
Constructor Summary
protected DefaultedMap(Map<K,V> map, Transformer<? super K,? extends V> defaultValueTransformer)
          Constructor that wraps (not copies).
  DefaultedMap(Transformer<? super K,? extends V> defaultValueTransformer)
          Constructs a new empty DefaultedMap that decorates a HashMap.
  DefaultedMap(V defaultValue)
          Constructs a new empty DefaultedMap that decorates a HashMap.
 
Method Summary
static
<K,V> DefaultedMap<K,V>
defaultedMap(Map<K,V> map, Factory<? extends V> factory)
          Factory method to create a defaulting map.
static
<K,V> Map<K,V>
defaultedMap(Map<K,V> map, Transformer<? super K,? extends V> transformer)
          Factory method to create a defaulting map.
static
<K,V> DefaultedMap<K,V>
defaultedMap(Map<K,V> map, V defaultValue)
          Factory method to create a defaulting map.
 V get(Object key)
           
 
Methods inherited from class org.apache.commons.collections4.map.AbstractMapDecorator
clear, containsKey, containsValue, decorated, entrySet, equals, hashCode, isEmpty, keySet, put, putAll, remove, size, toString, values
 
Methods inherited from class org.apache.commons.collections4.map.AbstractIterableMap
mapIterator
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
 

Constructor Detail

DefaultedMap

public DefaultedMap(V defaultValue)
Constructs a new empty DefaultedMap that decorates a HashMap.

The object passed in will be returned by the map whenever an unknown key is requested.

Parameters:
defaultValue - the default value to return when the key is not found

DefaultedMap

public DefaultedMap(Transformer<? super K,? extends V> defaultValueTransformer)
Constructs a new empty DefaultedMap that decorates a HashMap.

Parameters:
defaultValueTransformer - transformer to use to generate missing values.

DefaultedMap

protected DefaultedMap(Map<K,V> map,
                       Transformer<? super K,? extends V> defaultValueTransformer)
Constructor that wraps (not copies).

Parameters:
map - the map to decorate, must not be null
defaultValueTransformer - the value transformer to use
Throws:
IllegalArgumentException - if map or transformer is null
Method Detail

defaultedMap

public static <K,V> DefaultedMap<K,V> defaultedMap(Map<K,V> map,
                                                   V defaultValue)
Factory method to create a defaulting map.

The value specified is returned when a missing key is found.

Type Parameters:
K - the key type
V - the value type
Parameters:
map - the map to decorate, must not be null
defaultValue - the default value to return when the key is not found
Returns:
a new defaulting map
Throws:
IllegalArgumentException - if map is null
Since:
4.0

defaultedMap

public static <K,V> DefaultedMap<K,V> defaultedMap(Map<K,V> map,
                                                   Factory<? extends V> factory)
Factory method to create a defaulting map.

The factory specified is called when a missing key is found. The result will be returned as the result of the map get(key) method.

Type Parameters:
K - the key type
V - the value type
Parameters:
map - the map to decorate, must not be null
factory - the factory to use to create entries, must not be null
Returns:
a new defaulting map
Throws:
IllegalArgumentException - if map or factory is null
Since:
4.0

defaultedMap

public static <K,V> Map<K,V> defaultedMap(Map<K,V> map,
                                          Transformer<? super K,? extends V> transformer)
Factory method to create a defaulting map.

The transformer specified is called when a missing key is found. The key is passed to the transformer as the input, and the result will be returned as the result of the map get(key) method.

Type Parameters:
K - the key type
V - the value type
Parameters:
map - the map to decorate, must not be null
transformer - the transformer to use as a factory to create entries, must not be null
Returns:
a new defaulting map
Throws:
IllegalArgumentException - if map or factory is null
Since:
4.0

get

public V get(Object key)
Specified by:
get in interface Map<K,V>
Specified by:
get in interface Get<K,V>
Overrides:
get in class AbstractMapDecorator<K,V>
See Also:
Map.get(Object)


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